"Prices below $80 are putting significant strain on the cartel's weakest members such as Venezuela," said Nicolas Robin, a commodities fund manager at Threadneedle.
Read MoreSplit OPECexpectations may make for a volatile week
He said a bigger cut—of 1 million bpd or more—was an "outlier scenario," but such a move would rapidly push prices above $85.
"A move higher would likely be accelerated by the lack of liquidity owing to the U.S. (Thanksgiving) holiday next week," Robin added.
Doug Hepworth of Gresham Investment Management said: "A surprise significant cut, say of 2 million bpd, is needed to push prices back up to $80. And that would have to be accompanied by some new-found discipline in the non-Saudi members."
The market has been awash with conspiracy theories as to why Saudi Arabia has not already intervened. New York Times columnist Thomas Friedman hinted at "a global oil war under way pitting the United States and Saudi Arabia on one side against Russia and Iran on the other."
Read MoreOil traders increasebets on OPEC action
Tom Nelson, of Investec Global Energy Fund, said Saudi Arabia had allowed the price to fall to incentivize the smaller OPEC producers, which often rely on the biggest producer to intervene, to join Riyadh in cutting output.
"They (the Saudis) want to cut but they don't want to cut alone," Nelson said, adding that a cut of between 1 million and 1.5 million bpd should be sufficient to balance the market.
"The market really wants to see that OPEC is still functioning ... if there is a small cut, with an accompanying statement of coherence from OPEC that presents a united front, and talks about seeing demand recovery, and some moderation of supply growth, then Brent could move up to $80 to $90."